If you're unfamiliar with the premise, it's a travel-meets-reality show that sees seven couples, ensconced in a cramped coach, embark on a six-week jaunt around Europe. They embark on gloriously tacky tourist activities and vote off the pair they find most obnoxious at each destination, who are promptly replaced, Sugababes-style; a kind of Wish You Weren't Here.

Produced by the same people responsible for Eggheads (though arguably more cerebral), the programme is genius – though it's hard to say exactly why. It's partly in the casting: the participants' ages vary widely, from clubbers in their early 20s to those more likely to patronise the golf club. Unlike Big Brother, where inmates are helplessly attracted by the prospect of fame, you get the feeling the contestants here only want a free holiday, so they don't speak in reality-series language. High-grade entertainment is also provided by innuendo-splattering tour guide Brendan Sheerin, who comes across like an autocratic version of Coronation Street's Norris Cole; he becomes incandescent with rage whenever a bladdered holidaymaker fails to look thrilled by the world's largest glockenspiel, or whatever shonky attraction they're visiting that day.

Mainly, however, the attraction of the show is witnessing the contestants' cabin-fever hysteria, brought on by being forced to spend days on end cooped up in a confined space with flatulent, sweaty people they wouldn't let into their house. The businessmen in Deliverance had more chance of a quiet, uneventful vacation than these passengers do.

Previous highlights have included a pensioner being taught how to DJ in Ibiza by Brandon Block, thus putting the Grandma into Grandmaster Flash; a husband and wife disqualified for violence; and, best of all, an episode set mainly in a traffic jam, Sheering pushed to the end his tether by the passengers' repeated cries of: "Can I have a fag?"

The Coach Trip has been moved to a prize 5pm slot as an appetiser for the similarly well-edited Come Dine With Me, and the portents for hilarity have so far been good. Among the holidaymakers are a duo who describe themselves as "the British Will and Grace" (hopefully that doesn't mean it's actually their friends who are the funny ones); two indie-fringed teenagers necking smuggled-in absinthe that's 90% proof; and a Rochdale duo who insist on waving flags and whooping like banshees at every passing truck.

With a cult fanbase, The Coach Trip is tipped to become the next big crossover success. But please, Channel 4, don't transfer it to prime time. We don't want Sheerin becoming the next Jeremy Spake, or a shock twist where the sun-seekers discover that if the speed of the bus drops below 50mph, a bomb detonates. Let it remain a teatime guilty pleasure, and a reminder of why most of us prefer to go by plane.The Coach Trip is on Channel 4 on Tuesdays at 5pm, and More4 at 2.30pm.